Quadruple Giga

An ultimate skill, using all four spirits to destroy an enemy. If an attack is taken during the four turns of charging, it fails. In addition, all summoned spirits vanish when the skill is started.

“My sword swings through the air, with me barely managing to hold on. Flames and spouts of water shoot off my sword, as the wind tosses it around and the earth makes it almost too heavy to hold. Rather than balancing all four spirits, it’s almost like it’s a tug of war with them pulling in every direction at once. As I swing my sword down... The crazy power pulling my sword from every direction goes shooting straight into the ground! The ground splits in two with flames raging around the fissure, and cold gusts of wind blowing around the area. All four powers combined for a moment, and exploded in overwhelming power... I can’t even see the bottom of the split in the earth...” – Luka

“It’s an ultimate attack that uses all four spirits at once. First, point your sword toward the sky and summon the power of wind into your blade. Next... Put the power of the earth into your blade at the same time. Of course, without letting the power of wind dissipate. Next is water. Like the Earth and Wind, mix them together in your sword. ...Next, the power of fire. Concentrate all four elements in your sword. Now slash with your sword. The power of this skill is amplified by each spirit imbued in it. But if all four were at a power of ten, it wouldn’t be ten times four for forty... It would be ten to the fourth power for 10,000... This is the ultimate skill, Quadruple Giga. The skill takes a while to pull off. To get all four elements into your sword, it will take four turns. If you get hit in the meantime... Your concentration will fail, and so will the skill. One more issue... When you start the skill, any spirits you have summoned will vanish.” – Alice

“It’s a truly disgusting tale among monsters. The Hero Heinrich defeated Alipheese the Eighth with this skill. So that we would never experience a humiliating defeat from it again, it has been handed down among Monster Lords since Alipheese the Eighth's death. Ironically enough... It was never passed down among the human side, so it would have been safer to have let it fade into obscurity altogether. I’m entrusting it to you. Make sure you lead the world to peace using it...” – Alice

Quadruple Giga (カドラプル・ギガ Kadorapuru Giga) is Luka’s most powerful skill, taught to him before reaching the Monster Lord’s Castle on the night of his final camp by Alice. It is the second to last technique that he learns hitherto (Chapter 1 and 2). Using the combined power of the Four Spirits, it was the famed skill that Heinrich used to defeat Black Alice; Alice XVI only taught it to Luka so he could end her life. Granberia, having witnessed and even received a blow from the technique, is able to copy it.

It deals anywhere from 40,000–50,000 HP worth of damage, enough to finish off almost every single opponent in one hit. The technique also only costs 1 SP, allowing it to be activated virtually at any time.
However, it has numerous drawbacks which make the skill nearly unusable: It takes four turns to prepare, and if Luka is hit during any of these four turns, the attack will be canceled. Additionally, any spirits summoned will be deactivated upon use.

Due to these flaws, the skill only works against the following enemies:

Imp: An extremely lowly monster and thus can be attacked with Quadruple Giga. If defeated with this technique, a defeat message saying “even her screams were sealed” will be shown across the screen. Using Quadruple Giga against the Imp is an overkill, and is there solely for the sake of humor, as well as video game cruelty potential.

Tamamo (2): After using her Moonlight Cannon skill, Tamamo is exhausted and cannot continue the battle. Quadruple Giga can be used at this point.

Granberia (4): Once her health reaches the halfway mark, she will request Luka to use his ultimate attack; despite protesting how flawed it is, Granberia still wishes to see the technique. She will wait for Luka to prepare the attack, and Luka declares victory over her after this attack connects.

Alice (3): After Alice’s HP goes below 500 hp (499 is enough) and she requests Luka to finish her, this attack can be used to finish her off. This leads to a little extra dialogue which includes Alice lamenting over Black Alice’s defeat by Heinrich.

Runaeru: Heinrich shows off his power by using Quadruple Giga against the angel, who fails to stop him from charging it.

Arc-En-Ciel: Once her health is lowered by a fourth, Quadruple Giga is prompted. Granberia uses this technique to destroy her chimera counterpart, who misses a chance to stop Granberia from charging it.

Goddess Ilias (Final Form): Once Ilias's health reaches the near-end point, Alice tells Luka to use Quadruple Giga to finish her off. Ilias's attempts to stop the skill from charging are futile when Alice shields Luka. After applying all four elements to the skill, Alice tells him to infuse his holy energy within the skill, and she takes a hold of his weapon to infuse her dark energy. Holding their ideals of coexistence high and might, Luka and Alice strike down Ilias and the battle ends in a flash of light. Note that attempting to use Quadruple Giga before Alice's instruction will cause Ilias to instantly one-hit KO Luka with Ultimate Messiah, while completely disregarding the presence of his allies including Erubetie's Aqua Pentagram shield.

Trivia

This skill is the ultimate proof of mastery over the 4 spirits. Its concept and that of the four spirits is closely based on Fūrinkazan, a concept from Sun Tzu’sThe Art of War.

Quadruple Giga is the only Cursed Sword Skill created and used by a human rather than a monster.

However, when Luka learns Quadruple Giga, the earth effect from Earth Rumbling Decapitation is used.

Strangely, Heinrich and Granberia have been able to evade and even block attacks while loading Quadruple Giga, while Luka has to wait and cancel elements infused into his body in order to charge up the skill. Luka also mentions that Heinrich`s Quadruple Giga is twice as strong as his, at the least, despite the elemental powers being weakened at the time. While this can be attributed to their much longer experience in wielding the elements, Granberia was able to evade an attack on her first usage of Quadruple Giga.

Strangely, despite Goddess Ilias's and Micaela's claims of holy and dark energy being naturally incompatible with each other, Luka and Alice channel holy and dark energy into Quadruple Giga.

When used in the final battle against Ilias, Luka and Alice channel two more attributes into Quadruple Giga, increasing its strength by 10 to the 6th power, or 1,000,000. However, the damage dealt with the six infused attributes is not displayed.

When Luka and Alice interrogate Amira of her book "Legend of Hero Luka" which details everything from his adventurers, Alice mentions the final chapter is titled "The Hero and Monster Lord's final Love Love art: Love Lova Giga", an over-dramatic name of Luka and Alice combining their powers to use Quadruple Giga.